NRC decides unapproved software at nuclear plant isn't a risk

In this Fulton Sun file photo, taken during the Callaway Energy Center's 2015 maintenance and refueling outage, the nuclear facility's turbine is visible.
In this Fulton Sun file photo, taken during the Callaway Energy Center's 2015 maintenance and refueling outage, the nuclear facility's turbine is visible.

After the Callaway Energy Center's usage of unapproved computer software for a routine test triggered a Nuclear Regulatory Commission review, the NRC has decided there is no safety risk or wrongdoing.

A document summing up the issue was sent by John Klos, project manager for the plant licensing branch IV division of the Office of Nuclear Reactor Regulation.

According to the document, principally authored by Daniel Beacon and Carolyn Fairbanks, nuclear power plants put devices called "surveillance capsules" in the vessel surrounding the reactor core. These capsules measure exposure to neutron flux, or fluence, put off by the reactor core.

Over time, this bombardment weakens the vessel around the core, making it brittle. If it gets too brittle, it may fail. By testing the surveillance capsules, the plant can determine whether the vessel is still safe.

"The regulations require that nuclear power plants install and, at certain intervals, remove and analyze the changes in fracture toughness of the RV materials contained in the surveillance capsules," Beacon and Fairbanks wrote.

In October 2015, the Callaway plant - licensed by Ameren - pulled out Capsule W for analysis. However, the software used was RAPTOR-M3G, which the Nuclear Regulatory Commission hadn't approved.

"WCAP-14040-NP-A, Revision 4, specifies that the Discrete Ordinates Radial Transport code package (DORT/TORT), developed by the Oak Ridge National Laboratory, is to be used in reactor dosimetry calculations, such as those performed as part of the surveillance capsule report," the report stated.

NRC staff compared the RAPTOR-M3G results to other results determined using NRC-approved methods and ultimately determined that there was no safety issue. The staff also determined that "the submittal met the reporting requirements," meaning it contained all the necesary information.

"No further action from the NRC staff is warranted at this time," Fairbanks and Beacon concluded.